With the growing concerns over environmental impacts and the every increasing cost of energy products, both producers and consumers of reciprocating-piston engines are interested in means to improve the operational efficiency of these engines. Significant advancements have been made in the ability to tailor the operating characteristics of these engines in the areas of fuel delivery, ignition, induction and exhaust control.
A significant characteristic in the tuning of engines for efficient operation is the compression ratio. Historically, engines have been designed to a fixed compression ratio that is a compromise between the needs at multiple operating points (i.e. combinations of engine speed and load). Several mechanisms that allow the compression ratio to be varied during operation of the engine have been proposed, some of these solutions include a hydraulic mechanism that operates on the engine pistons or connecting rods to change the piston stroke. Two significant considerations in the design of such a hydraulic mechanism are: first, that the hydraulic fluid must be exchanged sufficiently frequently to prevent overheating of the fluid; and second, that overall flow of hydraulic fluid is preferably minimized so as to mitigate the pumping requirements (e.g. the energy consumed) and also to allow sufficient fluid to be exchanged in the limited time available during each engine cycle as the speed of the engine (i.e. revolutions per minute) increases. The previously known hydraulic mechanisms for varying the compression ratio typically either require large flows of hydraulic fluid (e.g. in some cases a continuous flow) or do not have provision to exchange the hydraulic fluid sufficiently often to prevent overheating of the fluid.
What is needed is a variable compression ratio system that provides for the compression ratio in a reciprocating-piston engine to be varied using hydraulic means where the overall flow of hydraulic fluid is minimized while being sufficient to provide for cooling of the fluid.